Freshwater eel populations are threatened due to overfishing and habitat degradation. Attempts to use aquaculture to sustain the fishery have often failed, owing to the complex lifecycle and the carnivorous nature of eel species. Monkeyface pricklebacks (Cebidichthys violaceus) have potential as an alternative cultivated finfish, possessing several characteristics warranting an assessment of the species that includes herbivory, potential high stocking density, tolerant of fluctuating environmental conditions, and no fishery competition. Though not technically an eel, C. violaceus is eel-like in appearance and is reported to taste like unagi. Their herbivorous, intertidal ecology has the potential to facilitate the use of fish free feeds and grow in warmer-than-ambient conditions. However, the ideal formulated diet and temperature to efficiently rear C. violaceus is unknown. To test this, we measured growth, feed intake, condition, metabolic rates, fillet composition, and critical thermal maximum (CTM) of juvenile monkeyface pricklebacks that were reared in separate experiments: (1) on four different diets (fresh seaweed, seaweed pellet, mixed pellet, and soy pellet) and (2) across five different temperatures (14-26℃) when fed the ideal diet.
Monkeyface pricklebacks exhibited the highest growth rates and body condition on the mixed and soy pellet diets and in the 20-23℃ treatment. Metabolic costs did not differ between diets, but they were impacted by temperature. FCR was lower on pellets and feed intake increased with temperature. Fillet composition was generally influenced by diet but not temperature. Fish could also increase their CTM by 2℃ after acclimating to warmer temperatures. If raised on a mixed and soy-based pellet at 20℃, monkeyface pricklebacks have the potential to increase their growth, which could reduce pressure on freshwater eel populations as farming increases the supply.